The present invention relates to a restarting device of a pump for automatically restarting an operation of the pump in such an event in which the operation of the pump is shut down due to a change-over valve stopping in an intermediate position, where such a valve is to be moved back and forth to switch a direction of movement of a center rod of the pump.
Some pumps, such as diaphragm-type pumps according to the prior art, for example, have employed such a configuration in which the pump comprises a center rod provided with diaphragms in both sides thereof for defining fluid delivering chambers and driving chambers, respectively. In such a pump, when the center rod is to be driven toward one side, a driving fluid (e.g., a compressed air) is supplied into the driving chamber located in one side of the center rod so as to discharge a fluid-in-transfer in the fluid delivering chamber located in that one side. The fluid-in-transfer is suctioned into the fluid delivering chamber located in the other side of the center rod while the driving fluid in the driving chamber located in the other side is discharged. When the center rod is to be driven toward the other side, the driving fluid is supplied into the driving chamber located in the other side of the center rod so as to discharge the fluid-in-transfer in the fluid delivering chamber located in the other side. The fluid-in-transfer is suctioned into the fluid delivering chamber located in the one side of the center rod while the driving fluid in the driving chamber located in the one side is discharged, so that the fluid-in-transfer may be transferred continuously by this reciprocating motion of the center rod.
The diaphragm-type pump is provided with a change-over valve which moves back and forth in order to switch a direction of movement of the center rod. Such a change-over valve has a spool. The spool is provided with a pair of pressure chambers each being disposed on each side of the spool along its direction of movement for switching the direction of movement of the spool. In the change-over valve, a differential pressure is generated between each of the pressure chambers at the terminal end of the moving stroke of the center rod so as to switch a position of the spool.
However, if the liquid prepared as the fluid-in-transfer includes air in it, the operation of the diaphragm may possibly become unstable so as to stop the spool of the change-over valve in an intermediate position along the direction of its reciprocating motion.
Further, in a case where there is an insufficient supply of the driving fluid, the differential pressure between each pair of the pressure chambers will decrease, and there will be a shortage of energy to move the spool, which thereby results in the spool stopping in an intermediate position along the direction of its reciprocating motion.
Further, in a case where a compressed air is used as the driving fluid, when the compressed air to be supplied to the change-over valve is delivered into the change-over valve, the pressure of the compressed air might possibly drop rapidly and cause a low temperature in the change-over valve by adiabatic expansion so as to lead to a partially frozen condition thereof, which thereby results in the spool stopping in an intermediate position along the direction of its reciprocating motion.
If the spool stops in the intermediate position, supply of the driving fluid to the driving chamber is stopped, and thus the operation of the pump is shut down. To solve this problem, an inventive attempt has been undertaken, in which a snap spring is attached to one end portion of the spool so that a bias force of the snap spring may be used to prevent, to the utmost possible, the spool from stopping in the intermediate position. However, there is still a possibility that the spool might stop its movement in an intermediate position along its reciprocating motion.
The present invention has been made in the light of the above problems, and an object of the present invention is to provide a restarting device of a pump for automatically restarting an operation of the pump in such an event where the operation of the pump is shut down due to a change-over valve stopping in an intermediate position, which valve is to be moved back and forth to switch a direction for a center rod of the pump to move.
According to a first aspect of the present invention, there is provided a restarting device of a pump in which the pump comprises a center rod having first and second fluid delivering chambers and first and second driving chambers defined at first and second sides thereof, respectively. When the center rod is driven in a first direction, a driving fluid is supplied into the first driving chamber so as to discharge a fluid-in-transfer in the first delivering chamber, and the fluid-in-transfer is suctioned into the second fluid delivering chamber while the driving fluid in the second driving chamber is discharged therefrom. Further, when the center rod is driven in a second direction opposite to the first direction, the driving fluid is supplied into the second driving chamber so as to discharge the fluid-in-transfer in the second fluid delivering chamber, and the fluid-in-transfer is suctioned into the first fluid delivering chamber while the driving fluid in the first driving chamber is discharged therefrom. As a result, the fluid-in-transfer may be continuously transferred by the center rod reciprocating in the first and second directions. The restarting device of the pump comprises: a change-over valve for switching a direction of movement of the center rod; and a restarting hydraulic circuit, wherein when a supply of the driving fluid from the change-over valve to the first and second driving chambers is stopped, the restarting hydraulic circuit detects the supply of the driving fluid in the first and second driving chambers having been stopped, and then causes the driving fluid to flow into the change-over valve, which thereby restarts the supply of the driving fluid into the first and second driving chambers.
According to a second aspect of the present invention, there is provided a restarting device of a diaphragm-type pump in which the diaphragm-type pump comprises a center rod provided with a first and second diaphragm each on opposite sides of the center rod. The first diaphragm defines a first fluid delivering chamber and a first driving chamber, and the second diaphragm defines a second fluid delivering chamber and a second driving chamber. When the center rod is driven in a first direction, a driving fluid is supplied into the first driving chamber so as to discharge a fluid-in-transfer in the first fluid delivering chamber, and the fluid-in-transfer is suctioned into the second fluid delivering chamber while the driving fluid in the second driving chamber is discharged therefrom. Or, when the center rod is driven in a second direction opposite to the first direction, the driving fluid is supplied into the second driving chamber so as to discharge the fluid-in-transfer in the second fluid delivering chamber, and the fluid-in-transfer is suctioned into the first delivering chamber while the driving fluid in the first driving chamber is discharged therefrom. As a result, the fluid-in-transfer may be continuously transferred by the reciprocating motion of center rod in the first and second directions. The restarting device of the diaphragm-type pump comprises: a change-over valve for switching the direction of movement of the center; and a restarting hydraulic circuit, wherein when a supply of the driving fluid from said change-over valve to the first and second driving chambers is stopped, the restarting hydraulic circuit detects whether the supply of the driving fluid in the first and second driving chambers has been stopped, and then causes the driving fluid to flow into said change-over valve, thereby restarting the supply of the driving fluid into the first and second driving chambers.
According to a third aspect of the present invention, there is provided a restarting device of a diaphragm-type pump in which said change-over valve has a spool having a direction of movement, and first and second pressure chambers are arranged along opposite ends of the direction of movement of the spool. The driving fluid is supplied respectively to the first and second pressure chambers to switch the direction of movement of the spool, wherein when the center rod reaches a terminal end of its moving stroke, a pressure difference is generated between the respective pressures of the first and second pressure chambers so as to switch a position of said spool.
According to a fourth aspect of the present invention, there is provided a restarting device of a pump in which the first and second pressure chambers are in communication with the first and second driving chambers via pilot valves, respectively. Further, when the center rod is to move in the first direction or the second direction, the position of the spool is switched in such a way that when the center rod reaches the terminal end of its moving stroke, the driving fluid in one of the pressure chambers in communication with its respective driving chamber having a decreased volume is discharged into its respective driving chamber so as to decrease the pressure in that one pressure chamber.
According to a fifth aspect of the present invention, there is provided a restarting device of a pump in which said restarting hydraulic circuit comprises: a three-way check valve unit for detecting a stopped supply of the driving fluid into the first and second driving chambers, a check valve unit, and a normally-closed valve unit for releasing the driving fluid from one of the first or second pressure chambers into the atmosphere. The three-way check valve unit has two suction ports and a discharge port. The check valve unit has a suction port and a discharge port. The normally-closed valve unit has an input port, a suction port and an output port. Each of the suction ports of the three-way check valve unit is in communication with the first and second driving chambers, respectively. The discharge port of the three-way check valve unit is in communication with the suction port of the check valve unit. The discharge port of the check valve unit is in communication with the input port of the normally-closed valve unit. The suction port of the normally-closed valve unit is in communication with one of the first or second pressure chambers, and the output port of the normally-closed valve unit is open to the atmosphere. The restarting device is characterized by the following. When the spool is in a reciprocating motion, the suction port and the output port of the normally-closed valve unit are isolated from each other by a pilot pressure, which is generated by supplying the driving fluid from the three-way check valve unit to the check valve unit so as to be applied to the input port of the normally-closed value unit. Further, when the spool operationally stops at an intermediate position along its direction of movement, the suction port and the output port of the normally-closed valve unit are brought into communication with each other due to a decrease of the pilot pressure caused by the driving fluid being released into an atmosphere via the three-way check valve unit and the check valve unit. As a result, the driving fluid is supplied to one of the first or second pressure chambers through the suction port and the output port of the normally-closed valve unit, so that a pressure difference is generated between the respective pressures of the first and second pressure chambers, thereby allowing the spool to move from the intermediate position where said spool has stopped.
According to a sixth aspect of the present invention, there is provided a restarting device of a diaphragm-type pump in which the restarting hydraulic circuit is incorporated in an interior of a main body of the diaphragm-type pump.
According to a seventh aspect of the present invention, there is provided a restarting device of a diaphragm-type pump in which the first and second pressure chambers are in communication with the first and second driving chambers, respectively, and when the center rod is to move in the first direction or the second direction, the position of the spool is switched in such a way that when the center rod reaches the terminal end of its moving stroke, the driving fluid is supplied in one of the pressure chambers in communication with one of the driving chambers which is different from the driving chamber not having a decreased volume in order to reduce the pressure in the other pressure chamber.
According to an eighth aspect of the present invention, there is provided a restarting device of a pump in which the driving fluid is a compressed air.